Distillation of fatty acids



pril 23, 1935.. L Ml TQLMAN DISTILLM'ION oF FATTY ACIDS original Filed Deo. 1, 1 32 2 Sheets-Sheet l WN EW 2 Sheets-Sheet 2 l L. M. TOLMAN DISTILLATION OF FATTY ACIDS Original Filed Deo. "l, 1952 April 23, 1935.

Patented Apr. 23, 1935 UNITED STATES PATENT OFFICE DISTILLATION F FATTY ACIDS Original application December 1, 1932, Serial No. 645,289. Divided and this application June 9, 1934, Serial No. 729,929

11 Claims.

The present invention relates to improvements in the distillation of fatty acids or of mixtures containing the same, together with fats or unsaponifiable matter, and will be fully understood from the following description illustrated by the accompanying drawings, in which apparatus suitable for carrying out the invention is diagrammatically illustrated.

In the distillation of fatty acids or mixtures containing them, in order to recover the fatty acids as distillates, as hitherto conducted, there are serious losses in the proportions of the fatty acids recovered, and a marked degradation of the undistilled residue. In general, in order to secure a high grade fatty acid product, it has been necessary to redistill the fatty acids recovered in such an operation, this redistillation being accompanied by a further loss. Such losses in the distillation operation and degradation of the products have persisted, notwithstanding the development of the use of high vacuum in the operation.

By operating in accordance with the present invention, it has been found possible to preventY the losses and avoid the deterioration of the products in the processes as hitherto conducted, thereby making it possible to dispense with further distillation of the fatty acid product while at the same time greatly improving the economy and efficiency of the distillation operation.

It has been discovered that a large part of the dilculty is due not only to an excessive time of heating, but to entrainment of particles of the undistilled residue in the distillate. 'I'his diiliculty has been in large part overcome and a distillate of higher purity and color obtained both by carefully controlling vapor velocity of the distillate and by careful removal of entrained matter.

In order that the invention may be fully understood it will be described in connection with the treatment of a suitable fatty acid stock, for example, the mixture derived by splitting the fats of a commercial grease or oil by any suitable process, such as the Twitchell process. Such a mixture, in ordinary practice, may contain 92% to 95% free fatty acids. When subjected to high vacuum distillation yaccording to the processes hitherto in use, the yield of fatty acid distillate in the first distillation is in the order of 85%, and on redistillation, the yield is in the order of 76% of the original stock.

In order that the process may be fully understood reference is to be had to the accompanying 5v5l drawings, in which:

Fig. 1 is an elevation, partly in section, of the apparatus.

Fig. 2 is a vertical section of the baille tower.

Fig. 3 is a horizontal section taken on line'3 of Fig. 2.

Fig. 4 is a horizontal sectiontaken on line 4 of Fig. 2.

In effecting distillation in accordance with the present process, the stock to be distilled is fed from a suitable source under pressure, for example, by a pump, (not shown) through line 5 into a pipe heater 6, which is heated in any sultable manner. In the form illustrated, the pipe heater 6 is shown as a coil in a lead bath 1 in a retort', heated in any suitable manner, as by the gas heater 9. In passing through the pipe heater 6, the oil is heated to a vaporizing temperature, ordinarily 400 F. or higher, say from 450 F. to 600 F., (the temperature employed depending in part on the vacuum employed in vaporization). While being heated, the oil is preferably maintained under pressure at the outlet of the coil, to avoid any substantial or excessive volatilization of fatty acids in the coil. In general, the coil outlet temperature should not exceed 650 F. The pressure maintained at the outlet of the coil, as shown by the gauge Il), may suitably be about 20 lbs. per square inch or higher, say 40 to 60 lbs., although much less pressure will suilice to prevent substantial Volatilization. At relatively lowA temperatures, only enough pressure, if any, need be used to regulate the flow.

After leaving the coil 6, the heated stock passes through a pipe I I to a manifold I2 from which it may bre discharged through either of lines I3, I4 or I5 into thetower I6. The lines I3, I4 and I5 are provided with pressure release and control valves II, I8 and I9 respectively, to permit the desired reduction in pressure on the stock as it enters the tower.

The tower I6 is provided internally with baffles or distributors 20 and 2I. The baille plates 20 may suitably be screen plates of the diameter of the tower and the baille plates 2I disk plates of smaller diameter. The form of the baille plate is of particular importance because the fatty acids have a remarkable tendency toward entrainment of the dark-colored portions of the undistilled residue. Even with low vapor velocities, which should not be materially over four feet per second at a high vacuum, and are preferably in the neighborhood of 2 or 3 feet per second, the tendency toward entrainment is very pronounced. The higher the vacuum, the greater is the permissiblev vapor velocity. At a 21-22 vacuum, a velocity of 2 to 21/2 feet per second is satisfactory, but even then only if proper entrainment-breaklng means are provided.

The type of entrainment-breaking means used will, of course, vary with the size of the still and other factors. By means of the present invention, however, distillate having a color on the N. P. A. scale of 3 or better may be produced on the first distillation. The following example gives a type which has proved exceptionally satisfactory, namely, such type as illustrated in Figs. 2-4 of the drawings. In the drawings, the tower IIS is preferably 30 inches in height (excluding the rounded ends) and of 6 inches internal diameter. The plate 22a is placed 41/2 above the bottom edge of the tower. Five inches above this is placed the baille 2I0. This baffle is a plate 4% in diameter and having three holes 1A nch in diameter placed 1% from the edge of the plate. The structure of the baille is shown in Fig. 4.

Five and one-fourth inches above the baille 2I0 is placed a screen baille 200, which is the full diameter of the tower. As shown in Fig. 3, the screen baille has a 1% hole at its center and three holes in diameter placed from the edge of the plate.

Six inches above baille 200 is another plate 2 I I, identical with 2I0. Five an one-fourth inches above baille 2II is another baille 20| identical with 200.

In this construction, the upper inlet I3a has a diameter of M1, and is two inches below the baille 200. The steam inlet 248L is a 1/ pipe, perforated on its lower side with small openings, through which the steam enters in a downward direction. The lower side of the steam inlet is 11/2" above the plate 22a. The inlet I4a is 3 inches above the screen 200 and the vapor outlet shown is the 1/2" outlet three inches above the baille 20|.

Some distance above the bottom of the tower I6, -a partition plate 22 is provided, through which passes the trapped overow pipe 23. Somewhat above the partition plate 22, a steam distributing pipe 24 is provided, to which superheated steam is supplied from the valve-controlled supply pipe 25.

The heated fatty acid-containing stock enters the tower through either line I3, I4 or I5 and preferably through an upper line I3 or I4, and is discharged thereinto at reduced pressure. The tower is maintained under substantial vacuum, preferably 20-22 inches or higher, as hereinafter more fully set forth. It descends the tower, meeting the superheated steam discharged into the tower from the distributor 24, and the fatty acid vapors rise to the top of the tower and pass out through the vapor line 26 to a condenser 21. The proportion of steam supplied may be varied in accordance with the vacuum employed and the proportion of fatty acids present in the stock. Thus, with a stock with the character hereinbefore referred to, and with the vacuum in the tower of about 22 inches, the proportion of steam to fatty acid may be approximately 40 to 60. It will be readily understood that with higher vacuum, less steam may be employed and also that the proportion of steam may be varied in accordance with the temperatures of operation and the nature of the fatty acids present. The outlet temperature at the top of the tower may vary from 375 to 550 F. with a vacuum of 22 inches, and with higher vacuum lower outlet temperatures may, of course, be employed; for example, as low as 350F.

The undistilled residue discharges continuously through the trapped outlet pipe 23 into the lower portion of the tower I6 below the partition plate 22, from which it may be withdrawn through the valved discharge line 28 into the container 29. When the latter is filled, the residue may be diverted to a second, similar container (not shown) while the rst residue container is vented to the atmosphere and its contents removed.

The fatty acid containing vapors discharged from the tower I6 through the vapor line 2S are condensed to liquids in the condenser 21 and discharged through manifold 30 and lines 3I and 32 to one of the receivers 33 or 34 respectively. 'I'hese receivers are employed alternatively, the one in use being disconnected from the system when it is filled and the other being then connected to the system. Each of the receivers 33 and 34 is connected by a valved line 35 and 35 respectively, to the vacuum manifold 31, which is connected to a suitable vacuum pump by which the desired vacuum is maintained upon the system, and uncondensed with vapor. It will be understood that the lines through which the heated stock passes from the heating coil to the tower, the tower itself and the lines leading therefrom, may be lagged or heat insulated.

By operating in the manner above set forth, from the stock hereinbefore described, it has been possible to produce in continuous operation a fatty acid distillate product with a yield of 92% (on the original stock) of a quality superior to that obtained in the second distillation in the processes as hitherto conducted. The fatty acid distillate is produced continuously of 'uniform quality and any portion thereof may be segregated and pressed, the admixture of earlier and later distilled portions to secure a pressable product not being necessary as in prior operations. At the same time, the residue of the distillation process is of an entirely different character from the pitch obtained in prior distillation processes and the saponiable constituents thereof may be recovered in a further distillation process.

For example, the tower shown in Figs. 2-4 was operated by heating 1.58 gallons of tallow grease per hour at a coil temperature of 600-630 F., and injecting 11.5 pounds of steam per hour into the tower at a pressure of 60-80 pounds and a temperature of 725-750 F, The tower was held under a 21" vacuum, and a temperature of approximately 500 was maintained at the top of the tower. Distillate was obtained at the rate of 10.4 pounds per hour, having the remarkably good color of 2 on the N. P. A. scale. This color is much better than is ordinarily secured by double distillation of the corresponding greases, even with a subsequent chemical decolorizing treatment. At the same time the yield produced was 87.1% on the basis of the stock introduced,

and approximately 92% on the acid content 'tillation of a commercial grease by my method The vapor velocity of the distillate leaving the tower in the example just given was approximately 2.15 feet per second on the average.

If this velocity is increased, with the same apparatus, the color will tend to become poorer. For example by operating at a tower temperature of 450 F., in a vacuum of 29", and feeding 2.15 gallons of tallow grease acids 'per hour, a color or 2% N. P. A. is obtained. In this instance, however, a yield of 92.6% on the original stock was obtained, as contrasted with 87.1% in the preceding example. The velocity in the last case was considerably higher than 2.15, but considerably less steam was used and the vvacuum was higher.

In the production of distillate of good color, it is particularly important that the undistilled residue be continuously removed from the tower. It has been discovered that if bottoms are allowed to accumulate in the tower, the color of the distillate rapidly becomes worse.

The temperature at the bottom of the tower is in excess of 550 F., and is, of course, distinctly below the temperature of the steam introduced. In the specific example heretofore given, the temperature at the bottom of the tower was of the order of 630 F.

In the construction of the apparatus, it is found that ferrous or predominantly ferrous metals may not be employed in the construction of the pipe coil and the distillation tower, as they are rapidly corroded. I have found that nickel or predominantly nickeliferous alloys, such as Monel metal, may be satisfactorily employed for the pipe heater 6 and the lines II, I2, I3, I4 and I5 through which the hot fatty acid-containing stock is conveyed to the tower. Either nickel or copper may be employed in the construction of the tower. By the use of a heating coil and transfer lines of copper or of nickel or nickeliferous material, I have found that the desired heating of the material may be affected without corrosion and without contamination of the distillate or residual products.

It is readily apparent that the process of the present invention may be employed under circum'stances in which the proportions of fatty acids present differ widely from those in the specific example set forth above; for example, in the separation of small proportions of free fatty acids from fats or oils in the production of refined or neutral fats or oils and in deodorizing fats and oils.

The fatty acid product produced by the dishas many new and improved characteristics. For example, the coolr of the product is far superior to the color of the fatty acids produced from equivalent stocks by former methods. 'I'he material is entirely odorless, so that acids from even the poorest garbage greases can be used in the manufacture of the better soaps; the iodine number, hydroxyl value, saponication number, peroxide number, acetyl value\ and practically all other tests show differences over fatty acid treated by former methods.

The most significant differences are in color and odor, and also ,in the crystal structure produced. The crystal of the new product is considerably superior to that produced in former fatty acids. The reasons for the exact nature of the diierence are not known, but the effect is readily noticeable. IIt has always heretofore been the practice to separate the oleic and stearic acid portions (so-called) by means of a preliminary cold pressing operation followed by a subsequent hot pressing. The stearic acid cake resulting from the nal hot pressing operation has always heretofore been fringed with a yellowish or yellowish red fringe which had to be broken off by hand. The portions so broken off were known as chips and amounted to about 7-10% of the total acids and to or more of the cake itself. 'Irouble with crystallization has been particularly noticeable heretofore in products which have been most carefully prepared. That is, if by extra treatment, a previous product of good color was produced, its crystallization was particularly bad. f

With the present process the crystal'is vastly improved over any product produced heretofore, and particularly over products of similar color. 'Ihe crystal structure is particularly remarkable in that no chips are formed, and the necessary labor, expense and loss occasioned by them is entirely eliminated. The resulting stearic acid in each case has substantially identical iodine number and titer, indicating clearly that the elimination of the chips is due to a different and better crystalline structure in the fatty acid.

Distillate produced by such a process differs under practically all tests from distillate produced from the same stock by the old bulk still process. For example, the following figures show a number of comparative tests on distillate produced by the old and the present process.

Analytical tests on products made on old and new type distillz'ng apparatus Original Test raw tallow Old stock Old still New stock Peroxide No Kreis test Reichert Meise! number.. Permanganate testi..

Acetyl value Heating test at 190 F Analytical tests on products old and new type distlling apparatus Old cold New cold Test pressed pressed Old red oil New red oll Old sicario New stearic Old foots New roots stock stock 103. 9 104. 2 99. 05 99. 98 105. 5 105. 5 50. 3 50. 2 9.0 9. 5 r129. 8 129. 7 23. 73 22.09 89.01 88. 52 6. 25 6. 34 3.00 1.97 27. 4 29. 3 None None la., 1 4. o 3% Sharp Faint Sharp Faint Very faint Very faint Peroxide No 2. 5 2. 5 75 1.

A 27B. 27B Kreis test QY gy The percentage yields of stearic acid and red oil portions from the old and new fatty acid product is shown in the following tables:

Yield figures of stearic acid and red oil from old andnew fatty acids This application is a continuation-in-part of my application Serial No. 484,895, filed September 27, 1930 and a division of my copending application Serial No. 645,289, filed December 1, 1932.

I claim:

1. The method of distilling a higher fatty acid from stock containing it which comprises rapidly heating a restricted continuously flowing stream of stock to a temperature of 400 F. to 600 F.; introducing the heated stock into an enlarged distilling zone under subatrnospheric pressure; introducing steam into the distilling zone in quantity and at a temperature to produce a temperature of 375 F. to 550 F. at the vapor outlet of the distilling zone, and causing the steam to contact with and travel countercurrent to the heated stock; withdrawing the steam and fatty acid vapors at the vapor outlet of the distilling zone at a temperature of 375 to 550 F. and continuously and separately removing the unvaporized residue from the distilling zone at a temperature above 550 F. and below 750 F. without maintaining a substantial body thereof within said distilling zone.

2. The process of claim l in which the residue is removed at a temperature of the order of 630 F.

3. The process of claim 1 in which entrained material is separated from the mixed steam and fatty acid vapor.

4. The process of claim 1 in which the residue is removed at a temperature of the order of 630 F. and in which entrained matter is removed from the mixed steam and fatty acid Vapor.

5. The method of distilling a higher fatty acid from stock containing it which comprises rapidly heating a restricted continuously owing streamof stock to a temperature of 400 F. to 600 F.; introducing the heated stock into an enlarged distilling zone under subatmospheric pressure; introducing steam into the distilling zone in quantity and at a temperature to produce a temperature of 375 F. to 550 F. at the vapor outlet of the distilling zone; causing the steam to contact with and travel countercurrent to the heated stock; withdrawing the steam and fatty acid vapors at said vapor outlet temperature at a vapor velocity as low as six feet per second for a vacuum of approximately twenty-two inches and continuously and separately removing the unvaporized residue without maintaining a sub stantial body thereof within said distilling zone.

6. The process of claim 5 in which the unvaporized residue is withdrawn at a temperature in excess of 550 F.

7. The process of claim 5 in which the mixed steam and fatty acid vaporis withdrawn at a velocity as low as approximately two to three feet per second for a vacuum of approximately twenty-two inches.

8. The process of claim 5 in which the mixed steam and fatty acid vapor is withdrawn at a velocity as low as approximately two to three feet per second for a vacuum of approximately twentytwo inches, and the unvaporized residue is withdrawn at a temperature in excess of 550 F.

9. The process of claim 5 in which the unvaporized residue is withdrawn at a temperature of the order of 630 F. and the mixed steam and' fatty acid vapor is withdrawn at a velocity as low as approximately two to three feet per second for a vacuum of approximately twenty-two inches.

10. A substantially odorless and colorless fatty acid product produced according to the process of claim 1 and containing mainly oleic, stearic and palmitic acids, said product having the property of producing a pressed cake under standard conditions of pressure and temperature having substantially uniform color throughout so as to require no chipping.

11. A solid fatty acid product comprising mainly stearic and palmitic acids of substantially uniform color throughout so as to require no chipping and having the crystalline characteristics produced by pressing under standard conditions of pressure and temperature from a substantially odorless and colorless fatty acid product containing mainly stearic, palmitic and oleic acids produced according to the process of claim 1.

LUCIUS M. TOLMAN.

Disclf-VMMER 1,998,997.- us M. Tolman, Chicago, Ill. DISTILLATION 0F FATTY ACIDS. Patent dated April 23, 1935. Disclaimer filed February 16, 1940, by the assignee, New Process Fat Refining Gorporation. f Hereb enters this diolaimer to claims 1, 2, 3, 4, 5, 6, 7, and 9 in said patent.

[ #1201211 Gazette March 5, 1940.] 

